In order to conserve energy in electronic circuits, particularly in battery-operated electronics, it is preferable to use bias currents which are no larger than necessary. Therefore, because the minimum required bias current tends to depend on signal amplitude, it is often desirable to use actual bias currents which are dependent on the amplitude of the signal. An additional advantage of amplitude-dependent biasing is that, if the bias current is only as large as needed, it will produce the least possible amount of noise (e.g., shot noise). These advantages have been discussed in the electronics literature with respect to at least one specific log-domain circuit. D. R. Frey and Y. P. Tsividis, “Syllabically Companding Log Domain Filter Using Dynamic Biasing,” Electronics Letters, vol. 33, no. 5, Aug. 28, 1997. Amplitude-dependent biasing can used in other circuits, e.g., amplifiers. However, one potential problem is that the bias can, in some cases, interact with the signal. Accordingly, there is a need for circuits in which the bias control and the signal properties are “orthogonal”—i.e., do not interact with each other.